Careful management of fertilizers on cropland in the Mississippi River drainage basin can help reduce the amount of harmful nutrients that flow down the Mississippi River and cause the annual Gulf of Mexico dead zone, but much more needs to be done.
Only about a third of the reduction can be reached through these fertilizer management activities, according to a new report in the Journal of the American Water Resources Association. The other two-thirds would require the construction of wetlands as well as having farmers plant cover crops. Both measures would help remove dead zone causing nutrients before they get to the river.
“Just doing fertilizer management will not be enough,” said Eileen McLellan, senior scientist with the Environmental Defense Fund and lead author of the article.
Dead zones are caused when nutrients from agriculture fertilizer or sewer systems get into the Mississippi River and then the Gulf of Mexico.
These nutrients help feed the growth of algae which uses up oxygen as it falls to the water bottom and decomposes. Without significant mixing from waves or other turbulence, this lower layer of water can see such low oxygen levels that it no longer supports life.
The researchers looked at the state of water quality and then considered what it would take to get to a 45 percent reduction.
That 45 percent is what the U.S. Environmental Protection Agency has suggested is needed to get to an average annual dead zone size of 1,930 square miles goal set by the Mississippi River Gulf of Mexico Watershed Nutrient Task Force.
Last year, this dead zone of low oxygen was measured at 5,052 square miles across the coast of Louisiana.
Each of the nutrient management and reduction strategies would work together to help pull out additional fuel for the dead zone and reduce the amount of nutrients coming off agricultural fields. Each one has its own challenges and expenses to complete, she said.
“Fertilizer management shouldn’t be too much of a challenge because that is something that is a benefit to farmers,” McLellan said. By being more selective about when and where fertilizer is applied, farmers can save money because less fertilizer is lost to runoff.
Cover crops are a little more challenging, but there seems to be a need for education for farmers on what and how to make this work, she said. Cover crops can either be a second commodity like barley or a plant that can be plowed under in the spring to provide nutrients for the next crop.
The real challenge will be in the wetland creation portion because that involves using some of a farmer’s land.
The report says that less than one percent of cropland in the Upper Mississippi-Ohio River Basin would be needed for the conversion to wetland to have an effect.
All three solutions share a common need: money.
“Money is part of the issue because it would cost a good amount,” she said.